(1) Field of the Invention
The present invention relates to a three-dimensional shape data processing apparatus that obtains three-dimensional shape data of an object and analyzes the features of the object.
(2) Related Art
Recently the technologies of obtaining three-dimensional shape data have developed. In such a technology, the spatial positions of a plurality of points on an object are obtained as three-dimensional shape data with, for instance, a range finder. Those obtained three-dimensional shape data are analyzed according to a mathematical method to be used in the analysis of physical features of the object.
The demand for obtainment of path lengths of paths along the surface of an object according to such three-dimensional shape data has increased. With the consumer demand for user-friendly products, custom-made clothes, shoes, glasses, and the like designed according to the three-dimensional shape model data obtained by measuring a human body have become popular recently. In this case, a plurality of characteristic points on a human body are designated and, for instance, clothes are designed according to the path lengths of the paths drawn through the characteristic points. In order to have the clothes fit the body, it is favorable to obtain not the sum of the lengths of straight lines between the characteristic points but the path lengths of the paths drawn through the characteristic points along the surface of the body.
It has been impossible, however, to obtain the precise path length of a path along a desired line on the surface of an object that has a complicated shape such as a human body according to such three-dimensional shape data.
As the analysis of the features of the object, the unevenness on the surface of the object is also calculated according to such three-dimensional shape data.
The three-dimensional shape data obtained by measuring an object with a range finder are only represented by a group of points that are spatially designated and the unevenness on the surface of the object may not be easily distinguished. As a result, it is necessary to obtain the characteristic amount representing the surface shape of the object, such as curvatures and differential values, and to evaluate the values quantatively.
According to the conventional manner, the characteristic amount such as a curvature at a vertex is calculated using the coordinates of the vertex and the surrounding vertexes in accordance with an approximate expression.
When obtaining three-dimensional shape data of an object, however, the intervals between the vertexes are irregular depending on the shape of the object or the measurement manner. More specifically, when measuring the shape of an object with a range finder, the surface of the object is measured by directing a beam in one direction that moves with regular intervals. As a result, the relationship between the direction of the optical axis of the beam and the direction of a normal of the surface is different for each sampling point, so that the intervals between sampling points on the surface of the object are irregular. As shown in FIG. 1, when sampling points on the surface of an object X by directing a beam in one direction at the surface of the object with regular intervals, the distance between points Pa and Pb and the distance between points Pc and Pd are different.
When the intervals between the vertexes (sampling points) are irregular, the accuracy of the characteristic amount at a vertex is different according to the area of the vertex on the object because the characteristic amount at a vertex on an area that has a relatively high vertex density is calculated according to the vertexes on a relatively small area and the characteristic amount at a vertex on an area that has a relatively low vertex density is calculated according to the vertexes on a relatively large area. As a result, the spatial frequency of the unevenness on the surface of the object is different according to vertex density.
Concerning characteristic amount, the characteristic amount at a vertex is affected by the degree of unevenness on the surface of an object. For instance, an outline of an object whose three-dimensional shape data have been obtained is the curved line on a two-dimensional plane as shown in FIG. 2a. The curved line has many small concaves and convexes due to the high-frequency noise of obtained data. When the data with high spatial frequency are removed, the curved line becomes smooth as shown in FIG. 2b. As a result, the characteristic amount such as the differential values at a point A in FIGS. 2a and 2b are different.
When an object has the uneven surface with many small concaves and convexes, the degree of unevenness on the surface of the object desired by the user depends on the needs. The user may desire to calculate the characteristic amount at a vertex on a smooth curved line with small spatial frequency or the characteristic amount at a vertex on an uneven curved line with small spatial frequency.
In a conventional manner, the characteristic amount at a vertex is calculated according to the coordinates of the vertex and the surrounding vertexes. As a result, the area on the surface of the object according to which the characteristic amount is calculated is fixed for each vertex. The characteristic amount at a vertex is calculated only according to the degree of spatial frequency determined by the density of the vertexes in the fixed area. As a result, it is impossible to flexibly calculate the characteristic amount according to the degree of unevenness.
According to a conventional manner, the characteristic amount that represents the surface shape of an object, such as a curvature and differential value, is calculated for three-dimensional shape data, which is represented by X-Y coordinates and the value of height, and is represented by the numeric value of the characteristic amount at the X-Y coordinates.
When the characteristic amount is represented by a numeric value, however, the concaves and convexes on the surface of an object may not be seen. The characteristic amount is calculated from three-dimensional shape data. As a result, when the characteristic amount is represented using two-dimensional X-Y coordinates, it is difficult to find the point at which the characteristic amount is located.
In addition, it is necessary to obtain the three-dimensional shape data of the object completely in order to analyze three-dimensional shape data precisely.
When measuring an object, some points on the object may not be measured due to the measurement direction, the light reflection on the surface of the object, and the color and the shade of the object. In this case, it is impossible to obtain the three-dimensional shape data of the points. When the three-dimensional shape data of some points on the object may not be obtained, it is impossible to analyze the physical features of the points and to calculate the volume of the object and the like.
According to a conventional manner, when the three-dimensional shape data of some points on the object are not obtained, the user edits a vertex as polygon mesh data or adding polygon mesh data with a hand process to supplement the three-dimensional shape data.
When the user supplements the three-dimensional shape data that has not been obtained with a hand process, the three-dimensional shape data is easily detected. At the same time, however, when the amount of data is large, the workload by the user is heavy. In addition, since the three-dimensional shape data is added on the two-dimensional image in the process, it is difficult to smoothly connect newly added polygon mesh data with the original polygon mesh data.